3:40 AM

SCADA Systems

Posted by Ravi

SCADA comes under the branch of Instrumentation Engineering. The term SCADA stands for Supervisory Control And Data Acquisition. Scada systems are used for controlling and monitoring chemical or transport processes and can be used in a factory environment such as electic power generation, water supply systems, gas and oil pipelines or any other distributed processes.

A typical SCADA system comprises of i/o signal hardware, controllers, software,networks and communication. SCADA system is normally used to monitor and control a remote site or a distribution that is spread out for a long distance. An RTU (Remote Terminal Unit) or a PLC (Programmable Logic Controller) is usually used to control a site automatically. The SCADA system also provides a host control functions for the supervisor to control and define settings.

For example, in a SCADA system a PLC can be used to control the flow of cooling water as part of an industrial process. At the same time the supervisor can use the Host control function to set the temperature for the flow of water. It can also have alarms and can record the flow of water temperature and report back to the SCADA system.

The RTUs and PLCs are responsible for data collection such as meter readings, equipment status etc and communicate back to the SCADA system. This data can be stored in a database for later analysis or monitored by a supervisor to take appropriate actions if required.

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either "hard" or "soft". A hard point is representative of an actual input or output connected to the system, while a soft point represents the result of logic and math operations applied to other hard and soft points. Most implementations conceptually remove this distinction by making every property a "soft" point (expression) that can equal a single "hard" point in the simplest case. Point values are normally stored as value-timestamp combinations; the value and the timestamp when the value was recorded or calculated. A series of value-timestamp combinations is the history of that point. It's also common to store additional metadata with tags such as: path to field device and PLC register, design time comments, and even alarming information.